Indonesia said on Saturday that fires across giant rainforests which caused Southeast Asia's worst air pollution crisis in years had been greatly reduced and were coming under control.

Indonesian Foreign Minister Marty Natalegawa gave the assessment after briefing his counterparts from neighbouring Singapore and Malaysia, the two countries most affected by the toxic smoke.

"The situation is more positive," Natalegawa told reporters after meeting Anifah Aman of Malaysia and Singapore's K. Shanmugam at an Association of Southeast Asian Nations (ASEAN) annual gathering in Brunei.

He said the affected areas on Sumatra island had dropped to 4,081 hectares, about one quarter of the size from when the fires were at their peak this month.

"So there's been a substantial reduction," he said.

"In other words, through a combination of efforts on the ground and from the air, in terms of seeding clouds and water bombing and propitious and friendly weather, I guess things are becoming more under control," he said.

"But we must continue these efforts... this is a commitment by the Indonesian government to ensure that we address this problem."

The so-called "haze" is an annual concern as traditional slash-and-burn farmers and modern corporate palm oil plantation companies burn Sumatra's forests and peat lands to clear land for agricultural use.

However this year has been the worst since 1997-1998, when haze caused an estimated $9 billion in losses in economic activity across Southeast Asia.

In recent weeks, Singapore has endured its highest air pollution levels on record, forcing residents to wear face masks and stay indoors.

The haze also raised diplomatic temperatures, with Singapore and Malaysia demanding that Indonesia do more to stop the problem.

They have pressed Indonesia to finally ratify a 2002 ASEAN agreement aimed at ending the haze. Indonesia is the only country in ASEAN not to have ratified it, although officials say it is currently before parliament.

Indonesia initially hit back at the complaints, saying some fires were on plantations owned by Singaporean and Malaysian business interests.

However Indonesian President Susilo Bambang Yudhoyono then apologised for the crisis, amid desperate efforts to put out the fires such as by trying to seed clouds to trigger rain.

Shanmugam, the Singaporean foreign minister, gave an upbeat assessment of the trilateral talks on Saturday, describing the discussions as "extremely positive" and "constructive".

"We are close neighbours, the three of us. And we have had a very constructive relationship all these years," Shanmugam said.

The issue is expected to be further discussed when the annual ASEAN talks officially get under way on Sunday, ahead of wider Asia-Pacific meetings involving the United States, China, Russia and other heavyweights.

Singapore and Malaysia have also demanded that Indonesia punish those behind the blazes.

Natalegawa said at least 18 people had been arrested, and vowed those found guilty would be "held accountable", but gave no further details.

AFP